function show_stairs(f, b)

figure;
if ~exist('b', 'var')
    b = zeros(size(f, 2), 1);
end
for i=1:size(f, 2)
    if b(i)
        line(f(:,i), [i;i], 'Color', 'red');
    else
        line(f(:,i), [i;i]);
    end
end

